Mike Taulty has posted a quick experiment that he has made with Silverlight 3 and navigation applications.
There are some new classes in the assembly System.Windows.Controls.Navigation.dll – specifically one called a Frame and a base class to derive from called Page along with some helpers of which the most key appears to be NavigationSource.
I built a little sample out of this. I wrote some .NET code that ran around my music library on my NAS and sucked out all the MP3 file information it could find and then I bundled that into an XML file and built a Silverlight app which shows that data.